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"Women and men who regularly trim or remove all their pubic hair run a greater risk of sexually transmitted infections," BBC News reports.

A survey of around 7,500 Americans, aged between 18 and 65 years, found "groomers" had a higher rate of sexually transmitted infections (STIs) such as herpes.

However, this doesn't necessarily mean that grooming pubic hair directly increases risk of STIs. The main limitation is that this study can't prove cause and effect. It could be the case that some people decided to remove their pubic hair after catching a STI.

And while the researchers took into account the number of lifetime sexual partners as a surrogate marker of sexual behaviour, they failed to assess the safe sex practices of participants. So any findings observed here are really only links to be assessed in further research.

The study speculates that grooming could lead to small cuts in the skin (microtears) which could make a person more vulnerable to catching certain types of STIs that can be spread via skin-to-skin contact, such as the human papilloma virus (HPV).

A study we discussed back in the summer found many women shaved their pubic hair as they mistakenly thought this was more hygienic. While you may choose to get rid of your pubic hair for cosmetic reasons, there is no evidence that doing so is good for your health.

Where did the story come from?

The study was carried out by researchers from The University of California and the University of Texas and was funded by the National Institute of Health and the Alafi Family Foundation.

The findings of this study have been widely reported in the UK media, however there was no mention of the fact that this research is not able to prove causation (cause and effect).

BBC News provides some useful tips on how to reduce your risk of catching an STI.

What kind of research was this?

This study was a cross sectional study which aimed to assess the relationship between pubic hair grooming habits and sexually transmitted infections.

Whilst this type of study is useful for finding possible links, studies that question exposures and outcomes at the same time are not able to prove cause and effect. There may be other factors at play which are responsible for the STIs.

Surveys are also subject to bias as the participants may not be entirely honest in their responses.

What did the research involve?

The researchers surveyed a sample of adults aged 18 to 65 years living in the US.

When invited to take part in the survey the participants were aware the subject of the survey was "Personal Grooming Injuries", however they did not have details of any questions in the particular survey until they accepted.

The survey was designed to assess the following:

pubic hair grooming practices

grooming injuries

sexual behaviours

STI history

Questions queried participants' grooming practices and included the following:

whether they had ever groomed (yes/no)

how often they groomed (daily, weekly, monthly, every 3 to 6 months or every year)

Participants were defined as "ever groomers" if they had ever groomed their pubic hair in the past, "extreme groomers" if they had removed all of their pubic hair more than 11 times per year and "high-frequency groomers" if they trimmed their pubic hair daily or weekly.

The participants were asked about their history of STIs, including the number and type of STIs. These STIs were categorised as either:

secretory (infections that can spread via body fluids), including gonorrhoea, chlamydia and HIV

Pubic lice were analysed separately.

The researchers made statistical adjustments for age and sex, and sexual behaviour variables such as frequency of sexual activity and number of sexual partners annually and over a lifetime.

What were the basic results?

In total 7,580 adults took part in the survey. Out of these, 74% reported pubic hair grooming, this was made up of 66% of men and 84% of women.

STIs were reported in 13% of participants (11% men and 15% women). Significantly more groomers reported a lifetime history of STIs than non-groomers (14% vs 8%).

Those who reported extreme grooming were more likely to report a lifetime history of STIs than those who reported non-extreme grooming (18% vs 14%).

No differences were observed between high-frequency and low-frequency groomers (15% vs 14%).

After analysing the survey findings and adjusting for the effects of age and lifetime sexual partners, "ever groomers" had an 80% higher rate of self-reported STIs (odds ratio [OR] 1.8; 95% confidence interval [CI] 1.4 to 2.2).

Cutaneous STIs were more than twice as likely in those who groomed (OR 2.6; CI 1.8 to 3.7), secretory STIs were 70% more likely (OR 1.7; CI 1.3 to 2.2) and lice 90% (OR 1.9; CI 1.3 to 2.9).

By type of cutaneous STI, grooming links were found for HSV, HPV and syphilis, but not for molluscum contagiosum which was reported by few people. For secretory STIs, links were found with chlamydia and HIV but not gonorrhoea.

How did the researchers interpret the results?

The researchers conclude: "Among a representative sample of US residents, pubic hair grooming was positively related to self-reported STI history. Further research is warranted to gain insight into STI risk-reduction strategies".

The team propose that a possible reason for this outcome is that grooming may cause epidermal microtears, which may increase the risk of STIs, particularly cutaneous, viral STIs. This mechanism was recently proposed for grooming and molluscum contagiosum.

Conclusion

This US questionnaire-based study aimed to assess the link between the grooming of pubic hair and lifetime history of STIs.

The findings showed that grooming was associated with a higher rate of STIs. The study has strengths in that it included a large number of both men and women with a very small number excluded from the analysis.

The team made attempts to make the survey as fair as possible and provided a laptop computer and free internet service to those without access to the internet. They also carried out a pilot survey to make sure it was valid and easy to understand.

However there are some important limitations to this research that overall mean that it can't prove conclusively that grooming pubic hair directly increases your risk of STIs.

By design this cross-sectional study is not able to prove cause and effect. It can't determine the timing of grooming compared to when STIs were acquired.

The study can't rule out the possibility that the link between grooming practices and STIs is being mediated by sexual activity (that is people who groom might be more sexually active and /or adventurous). The researchers failed to assess the safe sex practices of participants, they only used the number of lifetime sexual partners as a surrogate for risky sexual behaviour.

There is high risk of responder bias in a survey questioning such a sensitive topic – participants agreeing to take part in this survey may not be fully representative of the general public. That is, people with an active interest in the topic may be more likely to take part (which could explain the relatively high number of groomers in the study). Also, responders may not always be completely truthful in their answers.

There is the possibility of recall bias when participants were asked to recall both their past grooming habits and lifetime STIs – not all of which (for example, HPV or chlamydia) they may have been aware of having.

Overall, while the team attempted to control for possible confounding effects it is possible that some remained in the model and influenced these results.

Grooming of public hair itself is not going to cause a STI, but unsafe sexual activity can.

The best way to avoid sexually transmitted infections is to practice safe sex, including during anal and oral sex.

If you think you might have been involved in a risky sexual practice it's worth getting tested for STIs at a sexual health clinic, genitourinary medicine (GUM) clinic or GP surgery.

Some STIs, such as chlamydia, don't always cause obvious symptoms but can trigger complications, such as problems with fertility, further down the line.